What lies in between: Levallois, Discoid and intermediate methods
Guillermo Bustos-Pérez
What lies in between: Levallois, Discoid and intermediate methods
Guillermo Bustos-Pérez\(^{1,2,3}\), Javier Baena\(^{1}\), Manuel Vaquero\(^{2,3}\)
\(^1\)Universidad Autónoma de
Madrid. Departamento de Prehistoria y Arqueología, Campus de
Cantoblanco, 28049 Madrid, Spain
\(^2\)Institut Català de Paleoecologia
Humana i Evolució Social (IPHES), Zona Educacional 4, Campus Sescelades
URV (Edifici W3), 43007 Tarragona, Spain
\(^3\)Universitat Rovira i Virgili,
Departament d’Història i Història de l’Art, Avinguda de Catalunya 35,
43002 Tarragona, Spain
Abstract
The production of lithic artefacts is usually associated to different
knapping methods. Resulting flakes present metric and technological
features representative of the flaking method from which they were
detached. However, lithic production is a dynamic process where discrete
methods can be blurred, with features varying along the process. An
intermediate knapping method between discoidal and Levallois is commonly
referred under an umbrella of terms, presenting a wide geographical and
chronological distribution along the Early and Middle Palaeolithic.
Because this intermediate knapping method presents features from both
discoidal and Levallois knapping methods, this raises the question of up
to what point flakes from the three knapping methods can be
differentiated between each other and the directionality of confusions.
An experimental assemblage of flakes detached from the three methods is
employed along with attribute analysis and Machine Learning models to
identify the knapping method from which the flakes were detached. On a
general level results provide an excellent ability to differentiate
between the three knapping methods when a Support Vector Machine with
polynomial kernel is employed. Results also outline the singularity of
flakes detached from Levallois reduction sequences with an outstanding
value of identification, and being rare that they are erroneously
attributed to any of the other two knapping methods. Confusion between
discoidal and Hierarchical Discoid products is more common, although a
good value of identification is achieved for discoidal flakes and an
acceptable value is achieved in the case of Hierarchical Discoid flakes.
This shows the potential applicability of machine learning models in
combination with attribute analysis for the identification of these
knapping methods among flakes.
Keywords: lithic technology; experimental archaeology; Levallois; Discoid; Machine Learning; Middle Paleolithic
Extended abstract
La producción de lascas se asocia a diferentes métodos de talla. Las
lascas resultantes presentan características métricas y atributos que
son representativos del método de talla del que se han producido. Sin
embargo, la talla lítica es un proceso dinámico en el que los métodos de
talla definidos pueden verse entremezclados debido a adaptaciones a las
características volumétricas y de calidad de la materia prima,
diferentes fases a lo largo del proceso de reducción, aspectos
cronoculturales, etc. Esto da lugar a que las características de los
productos de talla varíen a lo largo del proceso de reducción. Bajo
diferentes términos es común encontrar alusiones a un método de talla
intermedio entre el discoide y el Levallois, presentando una amplia
distribución geográfica y cronológica a lo largo del Paleolítico Medio y
el Paleolítico Medio inicial. La concepción de este método de talla,
referido en el presente documento como Discoide Jerárquico, posee
características intermedias entre el Levallois (jerarquización de
superficies no intercambiables o un plano de talla paralelo a la
intersección de ambas superficies) y el discoide (ausencia de
preparación de talones, planos de talla secantes en la fase inicial de
talla), surgiendo la duda de hasta qué se pueden diferenciar los
productos de lascado de los tres métodos y sobre la direccionalidad de
las confusiones.
El presente trabajo emplea un conjunto experimental de lascas procedentes de los tres métodos de talla (77 del método de talla discoide, 73 del Levallois y 72 del Discoide Jerárquico). Sobre este conjunto experimental de lascas se realiza un análisis métrico y de atributos, y sobre los datos procedentes de este análisis se entrenan diez algoritmos de aprendizaje automático con el objetivo de determinar hasta qué punto es posible diferenciar el método de talla. Para evaluar los algoritmos de aprendizaje automático se tiene en cuenta la precisión general de los modelos, pero también los efectos del uso de umbrales de probabilidad en la identificación de los métodos de talla. El uso de umbrales de probabilidad permite optimizar el ratio de positivos verdaderos y positivos falsos para cada umbral de decisión y de ahí extraer el “área bajo la curva” (AUC en inglés) como valor de avaluación de un modelo.
De los diez algoritmos de aprendizaje automático, una máquina de vector soporte con kernel polinomial presenta los mejores resultados en la identificación de los tres métodos de talla, proporcionando unos resultados excelentes a la hora de diferenciar entre los tres métodos a nivel general (0.667 precisión, 0.824 AUC). Considerando individualmente cada método de talla, los resultados subrayan el carácter singular de las lascas procedentes de secuencias de reducción Levallois ya que obtienen una identificación excepcionalmente buena (AUC de 0.91), siendo su procedencia raramente atribuida a cualquiera de los otros dos métodos. La confusión entre productos procedentes de secuencias de talla discoide y el Discoide Jerárquico es más común, aunque se alcanza una identificación excelente en el caso de los productos procedentes de reducciones discoides (AUC de 0.82) y una identificación aceptable en el caso los productos procedentes del Discoide Jerárquico (AUC de 0.73).
Estos resultados muestran el potencial de combinar modelos de aprendizaje automático con análisis de atributos sobre lascas para la identificación de métodos de talla. Su uso puede servir de gran ayuda en la identificación de métodos de talla en lascas. Sin embargo, su uso requiere de una evaluación previa de los conjuntos líticos para determinar posibles métodos de talla existentes, uso diferencial de las materias primas, y evaluación de las cadenas operativas presentes.
Palabras clave: tecnología lítica; arqueología experimental; Levallois; Discoid; Paleolítico Medio; Aprendizaje Automático
1. Introduction
The Middle Paleolithic in Western Europe is characterized by the increase and diversification of prepared core knapping methods, resulting in flake-dominated assemblages (Kuhn 2013). These flake dominated assemblages are the result of a wide number of production methods which includes Levallois (Boëda 1994; Boëda 1995b; Boëda et al. 1990), Discoid (Boëda 1993; Boëda 1995a), SSDA (Forestier 1993; Ohel et al. 1979), Quina (Bourguignon 1996; Bourguignon 1997), different laminar production systems (Boëda 1990; Révillon & Tuffreau 1994), Kombewa (Newcomer & Hivernel-Guerre 1974; Tixier & Turq 1999) among several others. The abundance of different production methods results in a highly diversified material culture were flakes present a wide morphological variability. Flakes often retain morphologies and attributes characteristic of the knapping method from which they were detached, allowing for its identification. However, flakes often present overlapping attributes and morphologies as a result of the high internal variability of the methods and the ability for obtaining flakes with similar functional properties through different methods Kuhn (2013). Due to their wide geographical and chronological extension, Levallois and Discoid constitute an important source of cultural variability of the Middle Paleolithic from Western Europe.
Boëda (1994; 1995b) establishes six characteristics defining the Levallois knapping strategy from a technological point of view:
- The volume of the core is conceived in two convex asymmetric
surfaces.
- These two surfaces are hierarchical and are not interchangeable.
They maintain their role of striking and debitage (or exploitation)
surface respectively along the whole reduction process.
- The distal and lateral convexities of the debitage surface are
maintained to obtain predetermined flakes.
- The plane of fracture of the predetermined products is parallel to
the intersection between both surfaces.
- The striking platform is perpendicular to the overhang (the core
edge, at the intersection between the two core surfaces).
- The technique employed during the knapping process is the direct percussion with hard hammer.
Depending on the organization of the debitage surface Levallois cores are usually classified into preferential method (were a single predetermined Levallois flake is obtained from the debitage surface) or recurrent methods (were several predetermined flakes are produced from the debitage surface) with removals being either unidirectional, bidirectional or centripetal (Boëda 1995b; Boëda et al. 1990; Delagnes 1995; Delagnes & Meignen 2006).
Because of its early recognition in the XIX century (Boucher de Perthes 1857), its association with cognitive abilities of planning and predetermination (Boëda 1994; Pelegrin 2009), and its use for the definition of cultural facies (Bordes 1961a; Bordes 1961b) and lithic technocomplexes (Delagnes et al. 2007; Faivre et al. 2017), the Levallois flaking technology is considered a trademark of the Middle Paleolithic. Emergence of the Levallois method is observed from MIS12 to MIS9, with several sites presenting elements characteristic of Levallois production(Carmignani et al. 2017; Hérisson et al. 2016; Moncel et al. 2020; Soriano & Villa 2017; White & Ashton 2003). However, Levallois is clearly generalized and identified from MIS8 onwards, covering a wide geographical distribution throughout Western Europe (Delagnes et al. 2007; Delagnes & Meignen 2006; Faivre et al. 2017; Geneste 1990). The long geographical and temporary span of Levallois adds additional layers of variability which can result from raw material constraints, synchronic variability as a result of different site functionality, chronological trends in development of methods or shifts in the technological organization of groups. Attention is also called on the explicit recognition of Levallois cores after MIS 8, while a multitude of terms is employed to define previous hierarchical knapping strategies and its possible coexistence with Acheulean technocomplexes (Moncel et al. 2020; Santonja et al. 2016; Hérisson et al. 2016; Rosenberg-Yefet et al. 2022; White & Ashton 2003; Scott & Ashton 2011).
Boëda (1993; 1994; 1995a), also establishes six technological criteria defining the Discoid method:
- The volume of the core is conceived as two oblique asymmetric convex
surfaces delimited by an intersection plane.
- These two surfaces are not hierarchical being possible to alternate
the roles of percussion and exploitation surfaces.
- The peripheral convexity of the debitage surface is managed to
control lateral and distal extractions thus allowing for a degree of
predetermination
- Striking surfaces are oriented in a way that the core edge is
perpendicular to the predetermined products
- The planes of extraction of the products are secant
- The technique employed is the direct percussion with hard hammer.
Technological analysis of Middle Paleolithic assemblages has gradually led to identify a variability of modalities within the discoidal core knapping (Bourguignon & Turq 2003; Locht 2003; Terradas 2003; Locht 2003). This has resulted in sensu stricto and a sensu lato conceptualizations of the Discoid knapping system (Faivre et al. 2017; Mourre 2003; Thiébaut 2013). The sensu stricto highly corresponds to Boëda’s (1993) above mentioned definition, where core edge flakes and pseudo-Levallois points are the most common products. The sensu lato Discoid encompasses a larger range of products (although centripetal flakes are more common) as a result of higher variability in the organization of percussion and exploitation surfaces (Terradas 2003).
One of the variants from the Discoid sensu lato
conceptualization resembles Levallois knapping strategy (Figure 1). Some
common characteristics outlined for this method are:
1) The core volume is conceived as two hierarchical asymmetric surfaces:
the percussion surface and the exploitation surface (this is a common
feature with Levallois).
2) Preparation of the percussion surface is absent or it is partial,
without encompassing the complete periphery of the core. This can be a
result of raw material characteristics presenting an adequate morphology
or because it is achieved with minimal preparation.
3) Despite the hierarchical nature of both surfaces flakes detached from
the debitage surface present a secant relationship towards the plane of
intersection. Soriano and Villa (2017)
call attention that Levallois products usually present an external
platform angle (EPA) between 80º and 85º, while products from
non-Levallois hierarchical methods present an EPA relationship between
70 and 85º. However, this relationship can change along the core’s
reduction with final flakes being sub-parallel to the plane of fracture
(Slimak 1998).
4) Products from Hierarchical Discoid are usually symmetrical towards
the knapping direction, are thin, and the ventral and dorsal surfaces
present a subparallel relation. Again, these are common traits with
Levallois products.
Schematic representation of the knapping methods, surfaces and platform preparation
Strategies from several sites can be considered to fit the above mentioned variation of discoidal knapping method and its resemblance to the Levallois method has been previously noted for several Middle and Early Middle Paleolithic assemblages (Casanova i Martí et al. 2009; 2014; Jaubert 1993; Peresani 1998; Slimak 1998; 2003; Soriano & Villa 2017). However, it is important to consider that given the wide geographical and chronological span (Figure 2), different terms are employed. For Middle Paleolithic sites, the identity of this method usually focuses on the shared features with Levallois and Discoid and thus, its intermediate nature.
Jaubert (1993) at Mauran notes the hierarchical nature of the production system and its resemblance to exhausted recurrent centripetal Levallois cores. However, he points out the secant planes of detachment not so parallel as Levallois as a differentiation. Slimak (1998; 2003) at Champ Grand also notes the similarities of residual cores with recurrent centripetal Levallois debitage. Casanova i Martí et al. (2009; 2014) ) notes for Estret de Tragó the presence of products and knapping methods which share features of Levallois and Discoid, and proposes to include Hierarchical Discoid and Levallois recurrent centripetal strategies into the Hierarchical bifacial centripetal class. Peresani (1998) for Fumane cave notes the presence of debitage products with features (reduced thickness, debitage angle, and centripetal organization of scars also subparallel to the ventral surface) which would correspond to parallel planes debitage. Baena et al., (2005) indicate the presence of hierarchical Discoid along the sequence of Esquilleu cave as secondary and primary knapping method.
